Most people use the email analogy; the sub-lemmys are on different servers owned and moderated by different people, they just happen to use the same communication protocol. Similar to how you can email a hotmail, yahoo, or icloud account from a gmail account. And because they’re different servers people might have the same name, just differentiated by the server name. So you might see a MarySmith@gmail.com and a MarySmith@hotmail.com who aren’t the same person, they just happen to share a name.